Satan's role as leader in book 1, in which he makes some of his most famous statements, has been much debated since the Romantic era. As Milton explains and as Christian tradition tells us, Satan is the villain of the piece. However, because the epic begins with Satan and is initially told from Satan's point of view, we have a tendency to sympathize with him. Some Romantic poets, such as Wordsworth and Blake, saw him as the true hero of the poem, a being fighting tragically but heroically.
As book 1 shows, Satan breaks the chains that hold him to the lake of fire and brimstone in Hell, where God has cast him. He explains his management philosophy early on when he states,
Better to reign in Hell, then serve in Heav'n.
While he understands that he cannot win a direct war against God (he has just lost one), he decides to get revenge on God through an underhanded blow. He wants to corrupt the glory of God's creation, humankind, turning humans against God and breaking God's heart.
Satan shows he is a leader who is not willing to give up the fight, no matter how foolish and futile. He gathers around him his demons, fallen angels, who are described as a swarm of flies rather than a host of lovely, winged creatures. In Hell, Satan rules Pandemonium, a parody of the celestial city where God reigns in heaven. In it, he erects a garish palace.
In his pride, Satan cannot perceive that God is using him to orchestrate not just the fall but the ultimate redemption and triumph of humankind. Satan is the kind of destructive leader who would prefer to burn everything down than to see someone else win. Satan is a leader driven by spite, malice, and hate who cannot understand the true nature of God, but he nevertheless acquires some grandeur in his audacity in taking on God almighty.